Predation represents a significant selective pressure in most naturally living species. In primates, in particular, we now know that predation has played an important role in social group structure as well as in the patterns of diurnal and nocturnal activity. Most of our understanding of predation pressure in primates, however, comes from either uncontrolled natural observations of predation events or from controlled playbacks of predator alarm calls. Researchers have rarely attempted to present predators to primate subjects, and most of these involve stuffed models or silhouettes. While a few studies involve presentation or tracking of real predators, none of these involved the use of aerial predators. Since aerial predation represents a significant selective pressure on both ground and tree-dwelling primates, it is important to investigate how primates respond to such predation. The goals of this project are to understand the acquisition, refinement, and transmission of alarm responses to aerial predators by presenting a well-studied population of free-ranging rhesus monkeys with trained raptors that pose, as a function of size and distance, different degrees of threat.